Chengyu Mao

New heterometallic zirconium metalloporphyrin frameworks and their heteroatom-activated high-surface-area carbon derivatives.

Four cubic zirconium-porphyrin frameworks, CPM-99(H2, Zn, Co, Fe), were synthesized by a molecular-configuration-guided strategy. Augmentation of meso-substituted side arms (with double-torsional biphenyl rings) of tetratopic porphyrin linkers leads to a successful implementation of zirconium-carboxylate frameworks with cubic 2.5 nm cage. The hard-templating effect of Zr6-polyoxo-cluster and uniformly embedded (metallo)porphyrin centers endow CPM-99 with highly desirable properties as precursors for oxygen reduction reaction (ORR) catalysts. The pyrolytic products not only retain the microcubic morphology of the parent CPM-99 but also possess porphyrinic active sites, hierarchical porosity, and highly conducting networks. CPM-99Fe-derived material, denoted CPM-99Fe/C, exhibits the best ORR activity, comparable to benchmark 20% Pt/C in alkaline and acidic media, but CPM-99Fe/C is more durable and methanol-tolerant. This work demonstrates a new route for the development of nonprecious metal ORR catalysts from stable metalloporphyrinic MOFs.

Heterometal‐Embedded Organic Conjugate Frameworks from Alternating Monomeric Iron and Cobalt Metalloporphyrins and Their Application in Design of Porous Carbon Catalysts

DOI: 10.1002/adma.201500727 systems for the development of high-performance electrocatalysts. [ 10 ] The bimetallic catalysts with both Fe and Co can benefi t simultaneously from the unique graphene-rich morphology, enhanced corrosion resistance due to the presence of cobalt, and the intrinsically active FeN x sites, as shown by the earlier studies such as FeCo-EDA/C (EDA = ethylenediamine) by Choi et al., [ 10a ] FeCo-PANI/C (PANI = polyaniline) by Wu et al., [ 10b ] FeCo-OMPC (OMPC = ordered mesoporous porphyrinic carbons) by Cheon et al., [ 10c ] and FeCo-MFR/C (MFR = melamine-formaldehyde resin) by Zhao et al. [ 10d ]

In Situ Preparation of a Ti3+ Self‐Doped TiO2 Film with Enhanced Activity as Photoanode by N2H4 Reduction

A new synthetic method to fabricate Ti(3+)-modified, highly stable TiO2 photoanodes for H2O oxidation is reported. With Ti foil as both the conducting substrate and the Ti(3+)/Ti(4+) source, one-dimensional blue Ti(3+)/TiO2 crystals were grown by a one-step hydrothermal reaction. The concentration of Ti(3+) was further tuned by N2H4 reduction, leading to a greater photoelectrocatalytic activity, as evidenced by a high photocurrent density of 0.64 mA cm(-2) at 1.0 V vs RHE under simulated AM 1.5 G illumination. Electron paramagnetic resonance and Mott-Schottky plots reveal that higher charge-carrier density owing to N2H4 reduction contributes to the observed improvement. The generality of this synthesis method was demonstrated by its effectiveness in improving the performance of other types of photoanodes. By integrating the advantages of the 1D TiO2 architecture with those of Ti(3+) self-doping, this work provides a versatile tool toward the fabrication of efficient TiO2 photoanodes.

Systematic and Dramatic Tuning on Gas Sorption Performance in Heterometallic Metal-Organic Frameworks

Despite their having much greater potential for compositional and structural diversity, heterometallic metal-organic frameworks (MOFs) reported so far have lagged far behind their homometallic counterparts in terms of CO2 uptake performance. Now the power of heterometallic MOFs is in full display, as shown by a series of new materials (denoted CPM-200s) with superior CO2 uptake capacity (up to 207.6 cm(3)/g at 273 K and 1 bar), close to the all-time record set by MOF-74-Mg. The isosteric heat of adsorption can also be tuned from -16.4 kJ/mol for CPM-200-Sc/Mg to -79.6 kJ/mol for CPM-200-V/Mg. The latter value is the highest reported for MOFs with Lewis acid sites. Some members of the CPM-200s family consist of combinations of metal ions (e.g., Mg/Ga, Mg/Fe, Mg/V, Mg/Sc) that have never been shown to coexist in any known crystalline porous materials. Such previously unseen combinations become reality through a cooperative crystallization process, which leads to the most intimate form of integration between even highly dissimilar metals, such as Mg(2+) and V(3+). The synergistic effects of heterometals bestow CPM-200s with the highest CO2 uptake capacity among known heterometallic MOFs and place them in striking distance of the all-time CO2 uptake record.

Cooperative Crystallization of Heterometallic Indium-Chromium Metal-Organic Polyhedra and Their Fast Proton Conductivity.

Metal-organic polyhedra (MOPs) or frameworks (MOFs) based on Cr(3+) are notoriously difficult to synthesize, especially as crystals large enough to be suitable for characterization of the structure or properties. It is now shown that the co-existence of In(3+) and Cr(3+) induces a rapid crystal growth of large single crystals of heterometallic In-Cr-MOPs with the [M8L12] (M=In/Cr, L=dinegative 4,5-imidazole-dicarboxylate) cubane-like structure. With a high concentration of protons from 12 carboxyl groups decorating every edge of the cube and an extensive H-bonded network between cubes and surrounding H2O molecules, the newly synthesized In-Cr-MOPs exhibit an exceptionally high proton conductivity (up to 5.8×10(-2) S cm(-1) at 22.5 °C and 98% relative humidity, single crystal).

Size-Selective Crystallization of Homochiral Camphorate Metal–Organic Frameworks for Lanthanide Separation

Lanthanides (Ln) are a group of important elements usually found in nature as mixtures. Their separation is essential for technological applications but is made challenging by their subtly different properties. Here we report that crystallization of homochiral camphorate metal-organic frameworks (MOFs) is highly sensitive to ionic radii of lanthanides and can be used to selectively crystallize a lanthanide element into predesigned MOFs. Two series of camphorate MOFs were synthesized with acetate (Type 1 with early lanthanides La-Dy) or formate (Type 2 with late lanthanides Tb-Lu and Y) as the auxiliary ligand, respectively. The Ln coordination environment in each type exhibits selectivity for Ln(3+) of different sizes, which could form the basis for a new cost-effective method for Ln separation.

Hexagonal@Cubic CdS Core@Shell Nanorod Photocatalyst for Highly Active Production of H2 with Unprecedented Stability

A highly effective, low-cost strategy for improved photocatalytic efficiency and stability of CdS is described. Based on the integration of hexagonal-cubic core-shell architecture with nanorod morphology, the concentric CdS nanorod phase junctions (NRPJs) obtained demonstrate extremely high H2 production rate and unprecedented photocatalytic stability.

Generalized Synthesis of Zeolite-Type Metal–Organic Frameworks Encapsulating Immobilized Transition-Metal Clusters

Zeolites are generally made from tetrahedral nodes and ditopic linkers. Reported here is a versatile method based on trifunctional ligands. With this method, two functional groups are used to form zeolitic nets, while the third one serves to immobilize metal clusters within the channels. The process is driven by the coexistence of multiple inorganic building blocks generated in the heterometallic system. The generality of this method is shown by three distinct metal-organic frameworks mimicking AlPO(4)-5 (AFI) and BCT zeotypes as well as the cubic lcs topology. The correlation between the framework topology and trapped metal species reveals the unique bidirectional control (framework topology ↔ confined metal species) that may be exploited to create a large family of zeotypes with channels modified by different metal ions and clusters.

Monocopper Doping in Cd-In-S Supertetrahedral Nanocluster via Two-Step Strategy and Enhanced Photoelectric Response

We apply a two-step strategy to realize ordered distribution of multiple components in one nanocluster (NC) with a crystallographically ordered core/shell structure. A coreless supertetrahedral chalcogenide Cd-In-S cluster is prepared, and then a copper ion is inserted at its void core site through a diffusion process to form a Cu-Cd-In-S quaternary NC. This intriguing molecular cluster with mono-copper core and Cd-In shell exhibits enhanced visible-light-responsive optical and photoelectric properties compared to the parent NC.

An ultra-tunable platform for molecular engineering of high-performance crystalline porous materials

Metal-organic frameworks are a class of crystalline porous materials with potential applications in catalysis, gas separation and storage, and so on. Of great importance is the development of innovative synthetic strategies to optimize porosity, composition and functionality to target specific applications. Here we show a platform for the development of metal-organic materials and control of their gas sorption properties. This platform can accommodate a large variety of organic ligands and homo- or hetero-metallic clusters, which allows for extraordinary tunability in gas sorption properties. Even without any strong binding sites, most members of this platform exhibit high gas uptake capacity. The high capacity is accomplished with an isosteric heat of adsorption as low as 20 kJ mol−1 for carbon dioxide, which could bring a distinct economic advantage because of the significantly reduced energy consumption for activation and regeneration of adsorbents.